Massive Waste of Planetary Space?

[Nocturnal]

I know this must have been raised before but I couldn't find the search function. I just got a worse than useless tech from ruins: Massive Planetary Shield Generator.

This is a facility that provides my planet with a whopping 5000 shield points if I am not of sound mind and want to spend 30kT minerals, 1000 organics, 10kT radioactives and a precious building slot building it. Now, this didn't sound reasonable to me, so I fiddled with the designs window a bit, and found...

Two medium weapons platforms with: computer core, 8x shield generator V, 2x shield generator I, and one armor (just for kicks...) together cost 8940 minerals, no organics, and no radioactives. If you want to build a Cargo Facility to hold them, that's another 5000 minerals bringing the price up to 13940 minerals for the 5000 shield points, which my abacus tells me is still less than the 30000 minerals, 1000 organics, and 10000 radioactives it costs me to build the Massive Planetary Shield Generator facility. And the facility can't be picked up by my transport ships either.

Now given the above, would there be any reason in my right mind (which is debatable in itself but not the subject of this thread) that I would want to build this? If I'm incredibly low-tech in the beginning of the game and stumble upon this ruin, would it maaaybe then be a minor blessing and not be a terrible curse?

Is there some key rule I'm missing in the way the shields on a planet work? Or should I just mod that to be cheaper or something?